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Use Southern Cross to find due south

From the Northern Hemisphere, a fairly bright North Star marks the direction north. From the Southern Hemisphere, the Southern Cross points the way south.

The entire southern sky turns around the South Celestial Pole, captured here behind the antennas of the Atacama Large Millimeter/submillimeter Array in Chile. Draw a line directly down to the horizon from South Celestial Pole to find the direction due south. Babak Tafreshi, a Photo Ambassador for the European Southern Observatory (ESO), took this photo. Image via ESO; read more.

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Steve Brown wrote:

I realise that the majority of your readers reside in the Northern Hemisphere and fewer in the Southern Hemisphere. Is your community aware that the constellation of the Southern Cross (which appears on both the Australian and New Zealand flags) can be used to point out the South Celestial Pole and the direction south?

Steve also provided many links and references to finding south with the Southern Cross. Thank you, Steve! Here we go …

This is the constellation Crux, aka the Southern Cross. Image via ESO/Yuri Beletsky

The north and south celestial poles lie above Earth’s north and south poles. Image via OneMinuteAstronomer.com.

The south celestial pole is the point in the sky directly above Earth’s southern axis. It’s the point around which the entire southern sky appears to turn. The height of the south celestial pole in your sky depends on your latitude. The sky’s north pole has a moderately bright star – the North Star, aka Polaris – approximately marking its location. The sky’s south pole has no such bright star. But, if you’re in the Southern Hemisphere, you can indeed use the Southern Cross – also known as the constellation Crux – to find celestial south. Then you can draw a line downward from celestial south to find the direction due south.

The Australian Broadcasting Corporation (ABC) published the following two illustrations showing how to use the Southern Cross to find the south celestial pole and the direction south:

Imagine a line joining the two stars at the ‘head’ and the ‘foot’ of the cross. Extend the line out another four lengths from the foot of the cross to the south celestial pole. Then look straight down from the south celestial pole to the horizon. You’ve found south! Illustration and caption via ABCScience.

Another slighty trickier, but more accurate, way of finding south is to use the Southern Cross and the pointer stars from the neighbouring constellation, Centaurus. Draw a line through the two stars at the ‘head’ and the ‘foot’ of the cross and extend it to the dark patch of the sky the same way as in the first method (Line 1). Then join a line between the two pointers (Line 2). Find the middle of Line 2 then draw a perpendicular line down toward Line 1 until the lines meet. The point at which the lines 1 and 3 intersect is the south celestial pole. From there just look straight down to the horizon and you’ve found south. Illustration and caption via ABCScience.

Prefer to get your information via video? Here are a couple of videos showing the same thing, how to use the Southern Cross to find the south celestial pole and due south:

The Southern Cross isn’t the one route to finding celestial south and the direction due south. There are several others way to find south. If you’re interested, try this Wikipedia page. The illustration below, which I found on Wikimedia Commons, shows how to use the Large and Small Magellanic Clouds to find celestial south.

Happy gazing, southern friends!

You can also find the South Celestial Pole, and due south, using the famous Large and Small Magellanic Clouds. These ‘clouds’ are actually satellite galaxies orbiting our own larger Milky Way galaxy. If you spot them on a clear, moonless night in the Southern Hemisphere, make an equilateral triangle, the third point of which is the South Celestial Pole. Image via Michael Millthorn/ Wikimedia Commons.

Our annual fund-raiser ends May 5. EarthSky needs your help to keep going! Please donate!

Want to donate via PayPal or send a check to EarthSky? Click here.

Bottom line: Illustrations and videos showing how to use the Southern Cross to find the south celestial pole and the direction due south.

Deborah Byrd

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